It doesn't mean strongest bar none and never will because there is a title that supercedes the WSS title, and that is Worlds Strongest Man. A title that didn't default to Mihawk after Whitebeard death. That title will go to Blackbeard as foreshadowed by his comment after getting the Gura fruit, that with it he truly is the Strongest.
For starters nothing implicates that a WSS cannot stand as WSM. Second, nothing implicates that the WSS * necessarily * needs to stand as WSM as long as WSM is no swordsman.
For example I'm one of the few who classify Whitebeard as a swordsman due seemingly being the carrier and heavy user of a supreme grade sword, and yet I don't believe he necessarily always perpetually stood as WSM despite the vivre card kept suggesting such notion and that is due his sickness taking over. Titles don't necessarily have to work out in real time, MF profusely demonstrated how Whitebeard was probably no more the WSM.
That being said it is common in a fictional work that the strongest swordsman is catalogued by the author as most powerful as well, not merely best at sword skill. On top of it, it would make sense if Mihawk was the strongest given he's Zoro's final set opponent and as a kid he swore he had to become the World's strongest. Yes he specifically mentioned this, confirmed by Oda himself.